/Engine/Source/Runtime/Engine/Classes/Engine/World.h
Given a PackageName and a PIE Instance ID return the name of that Package when being run as a PIE world
static [FString](API\Runtime\Core\Containers\FString) ConvertToPIEPackageName ( const [FString](API\Runtime\Core\Containers\FString) & PackageName, int32 PIEInstanceID )